Instructions
Check to see if your female cat is in heat. A female cat generally starts her first heat cycle when she is six months old, which means that she is now capable of reproduction. A cat in heat will generally bleed from the vagina, frequently rub up against you and other objects and be more vocal. If a female cat is spayed when she is a kitten, however, she will be incapable of reproduction and thus it's unlikely that she will exhibit any such signs.
Consider the cat's age. A cat is considered to be an adult when it becomes 1 year old. Many cats will stop growing around this age, thought a few select breeds will continue to grow up until the cat is 5 years old. If you have owned the cat since it was born or know the month in which it was born, you can then determine when it will turn 1 and thus when it will become an adult.
Watch for changes in the cat's behavior. Adult cats behave slightly different than kittens in that adult cats sleep longer and more frequently. Fully grown cats still might play from time to time but not as often as a kitten would. Many adult cats sleep at least 50 percent of each day, if not more, while a kitten will usually nap slightly less than that.
Think about the cat's affection for you. Nearly every cat gets more affectionate toward its owner as the cat ages. Younger kittens are generally too busy exploring, playing or being independent to be snuggly and affectionate. As a cat grows older, becomes more tired and gets used to being on its own, it commonly will want to spend more time with the owner.
How to Know If a Female Cat Is Fully Grown
Just like humans, cats continue to grow and act differently as they mature. If you're the owner of a new cat, you may wonder how to tell when a cat is fully grown. It's slightly easier to tell when a female cat is fully grown because of the way she acts as she approaches sexual maturation. Behavioral factors and other considerations also come into play when determining when a female cat is fully grown.